1. Field of the Invention
The invention relates to photo-optical keyboards. More specifically, the invention relates to an improved keyboard housing and keys which provide an N-key rollover feature.
2. Description of the Prior Art
One of the problems associated with photo-optical keyboards is the problem of "blind spots". This occurs when an operator has one key depressed and keeps it depressed while depressing a second key. The first key blocks the light channels for a row and a column. If the second key is in one of these two light channels, the depression of the key will not be registered. This problem is resolved by having an N-key rollover feature. This feature allows any number of keys to be depressed within a given time while the output signal will be in the order of key depression regardless if previously depressed keys are released. U.S. Pat. No. 3,796,880 describes one method for incorporating the N-key rollover feature in a photo-optical keyboard. This method involves using decoding circuitry to determine if two keys have been depressed at the same time. The circuitry, however, is complex and expensive.